"We knew there was some association between psoriasis and diabetes and high blood pressure," says Abrar Qureshi, MD, MPH, assistant professor of dermatology at Harvard Medical School and a dermatologist at Brigham and Women's Hospital, Boston. "The question was, which came first."

In the study, he tells WebMD, "We were able to show women with psoriasis had a higher risk of developing diabetes and hypertension."

The study is published in the April issue of the Archives of Dermatology.

Qureshi and colleagues studied 78,061 women who participated in the Nurses' Health Study II, a long-running study that first collected data in 1989 from more than 116,000 women (all registered nurses) and followed up with questionnaires about their health every two years.

All were free of diabetes and high blood pressure at the study's start. In 2005, the women reported whether they had ever gotten a diagnosis of psoriasis from a doctor. After excluding the women who already had diabetes or hypertension, the researchers focused on 78,061 women, including 1,813 with a diagnosis of psoriasis.

Psoriasis affects up to 3% of the population, according to the researchers. Five types occur, according to the American Academy of Dermatology, with different symptoms and signs. The most common is plaque psoriasis, marked by itchy patches of red, raised skin covered by a silvery-white scale that shows up most often on the elbows, knees, scalp, and lower back.

Psoriasis and the Link With Hypertension and Diabetes

The researchers followed the women who had a diagnosis of psoriasis for 14 years to determine if those were more likely to develop diabetes and high blood pressure.

The results: the women who had psoriasis were 63% more likely to get diabetes and 17% more likely to get high blood pressure.

This was true even after accounting for such factors that could boost the risks of the other conditions, such as obesity and smoking status.

"We were surprised to see the numbers so high, especially for diabetes," Qureshi says.

Why the link? Qureshi says it may be underlying inflammation, thought to play a role in all three diseases. His team will try to duplicate the study in men to see if the link holds.

Though previous studies have also found a link between the three diseases, Qureshi says they were studies that looked only at one point in time, while his study has a long follow-up period and many participants.

It's not known whether anti-inflammatory treatments can reduce the risk of getting the other diseases, he says. The research does suggest that psoriasis should be viewed as not just a skin disease, but as a systemic disorder, he says.

Qureshi's study was partially funded by the National Cancer Institute. He has served as a consultant and speaker for the drug companies Abbott, Amgen, and Genentech.

Second Opinion

The new study adds to the credibility of the link between psoriasis and other disorders, according to William H. Eaglstein, MD, emeritus chair of the department of dermatology and cutaneous surgery in the Miller School of Medicine at the University of Miami. Eaglstein wrote an editorial about the Qureshi study and other research.

The follow-up design was important to find the link, he tells WebMD, as was the large sample size. "The size was probably needed to make the connection," he says.

Whether the link is due to inflammation alone or something else combined with the inflammation is not known, says Eaglstein, who is also vice president of global medical science for Stiefel Laboratories Inc., a pharmaceutical company that makes skin care products.

Until more is known about the link between psoriasis, diabetes, and blood pressure problems, he says, "The take-home message is that both patients and physicians should be alert to the possibility."